In the field of polymeric coating, it is often desirable to place coatings of relatively high quality onto surfaces of complex shape, or surfaces that are not readily available to known coating methods, such as were surfaces that are in some way sequestered. Sequestered surfaces for example may be those on complex shapes, or those on multicomponent parts, such as car parts that are already assembled. In this regard, in industries such as the automobile industry, it is often desirable to be able to place a high quality coating on an automobile part (such as a body trim part) after it has been affixed to the automobile. One of the advantages of being able to coat such a part after assembly is that the risk of damage to the surface occasioned by its handling, or the use of fixtures, may be substantially reduced or eliminated.
In these instances, the automobile part may not be in a position to allow a coating to be cured effectively in situ by light or heat as a curing agent, or by the application of a chemical curing agent in a liquid form, in large part because portions of the surfaces, in addition to their complexity, cannot be reached or reached efficiently by any such curing agent.
In these and other applications, an assembled part may be near another material that might be damaged by use of any such curing agent.
Accordingly, there remains a need for methods to allow one to apply high quality coatings to surfaces of complex shapes or surfaces that otherwise are sequestered such that known techniques cannot be used or used efficiently. One example of such high quality coatings are those that involve thin coatings, including those that require especially high degree of uniformity and complete coverage of the surface.
Many applications in the modern coating industry can be improved if direct use of light and/or heat is avoided. Other applications require polymerization of heat sensitive materials in the locations which are not efficiently accessible for light. Still others may require polymerization where direct use of light and/or heat cannot be used efficiently. Accordingly, the present invention provides polymerization without direct use of light and/or heat representing an improvement over polymerization and cure systems of the prior art in the area of coatings.
Borane chemistry has been studied in great detail (for example see: Onak T. Organoborane Chemistry Academic Press: New York, 1975 and Brown H. C. Boranes in Organic Chemistry Cornell University Press: Ithaca, N.Y. 1972 (all incorporated herein by reference)). One of the most important properties of trisubstituted boranes is to initiate and catalyze the polymerization of the vinyl monomers. The mechanism of organoborane action has been a subject of several reports (for example see: H. C. Brown and M. M. Midland, Chemical Commun., p. 699 (1971); F. J. Welch, J. Polym. Sci., vol. 61, pp. 243-252 (1962); and M. F. Sonnenschein, S. P. Webb, P. E. Kastl, D. J. Arriola, B. L. Wendt, D. R. Harraington, N. G. Rondan, Macromolecules, vol. 37, p. 7974 (2004) (all incorporated herein by reference)).
Mottus et. al. (U.S. Pat. No. 3,275,611 (incorporated herein by reference)) describes polymerization of olefins activated by the combination of organoborane, peroxygen compound and amine that could be added to the polymerizable resin together or separate. Many compositions are reported to be pyrophoric and display only marginal adhesion to the low energy surface substrates.
Skoultchi et. al. (U.S. Pat. Nos. 5,106,928; 5,143,884; 5,286,821; 5,310,835; 5,376,746 (all incorporated herein by reference)) describes two-part system for acrylic adhesive compositions involving activating of borane-amine complexes present in the first part by either carboxylic acids or aldehydes from the second part upon physical mixing.
The series of patents issued to Zharov et. al. (U.S. Pat. Nos. 5,539,070; 5,690,780; 5,691,065 (all incorporated herein by reference)) discloses a two-part adhesive systems utilizing borane-amine complexes with alkanol amines being the primary complexing agents.
Pocius et. al. (U.S. Pat. Nos. 5,616,796; 5,621,143; 5,681,910; 5,686,544; 5,718,977; and 5,795,657 (all incorporated herein by reference)) describes a two-part system for acrylic adhesive compositions containing borane-amine complexes with N:B atom ratio of 4 or less. Various amines, polyamines, and polyols are described as complexing agents. Isocyanates are disclosed as release agents to decomplex organoborane.
Other two-part adhesive systems for low surface energy substrates are described by Sonnenshein et. al. (U.S. Pat. Nos. 5,616,796; 5,621,143; 5,681,910; 5,686,544; 5,718,977; 5,795,657 (all incorporated herein by reference)), Deviny et. al. (U.S. Pat. Nos. 5,872,197; 5,990,036; 5,883,208; and 6,762,261 (all incorporated herein by reference)) and Moren et. al. (U.S. Pat. No. 6,734,268 (incorporated herein by reference)). In these disclosures, various borane-(mono, poly) amine complexes in the first part of the composition are activated by mixing with the second part of the composition containing various release agents (acids, acid anhydrides, acid halides, aldehydes and isocyanates).
Moren et. al. (U.S. Pat. No. 6,486,090 (incorporated herein by reference)) further discloses the utilization of hydroxide or alkoxide anions as complexing agents for borane with decomplexers selected from isocyanates, acids, acid chlorides, sulfonyl chlorides, or anhydrides.
Maandi et. al. (U.S. Pat. No. 6,867,271 (incorporated herein by reference)) proposes the stabilization of hydroxy-, alkoxy- and tetraalkyl borates and alkyl borohydride salts of alkali metals and quaternary ammonium cations within an inert carrier (i. e. tetraglyme) to which some aziridine containing compounds are added. The first part of the composition containing the stabilized borate initiator is mixed with the second part containing polymerizable resin with borate activation occurring upon mixing.
Many of polymerizable compositions described in the prior art demonstrate excellent properties including stability, strength and adhesion. However, all compositions previously reported are two-part compositions that require physical mixing of two condensed phases. This is disadvantageous because the control of the cure is limited, cure times are long, and application of the formulations to sequestered surfaces (including those surfaces where efficient or uniform application of light or heat is difficult). A more general coating process is needed that takes advantage of the useful properties of borane-amine complexes, uses the single formulation applied to the substrate, and eliminates all the disadvantages resulted from the use of two-part compositions.